The present invention disclosed herein relates to an electric field emission device such as an X-ray tube, and more particularly, to a method of more efficiently driving a plurality of electric field emission devices and a multi electric field emission system.
A tomosynthesis imaging system typically uses a plurality of electric field emission X-ray tubes.
An electric field emission device configuring an electric field emission X-ray tube includes a cathode where an emitter emitting electrons is formed. Once electric field is applied to the cathode of the electric field emission device, electrons are emitted from the emitter and are attracted to an anode. The electric field applied to the cathode is determined by a voltage of an anode in the case of a bipolar structure and by a gate voltage in the case of a tripolar structure.
In order for stable driving, a current flowing in an electric field emission device needs to be controlled to be constant. In order to control a current of an electric field emission device, a method of controlling a voltage applied to the electric field emission device is provided. However, the current of the electric field emission device is exponentially increased in correspondence to an applied voltage. Additionally, since the characteristic of the emitter of the electric field emission device may be deteriorated or activated as time elapses, a current emitted with respect to the same voltage may be decreased or increased. Accordingly, in general, it is difficult to constantly controlling an electric field emission current by using a voltage applied to an electric field emission device.
Accordingly, a technique of controlling an electric field emission current of an electric field emission device with a constant value by using a current control circuit is developed. That is, such a current control circuit directly controls a current flowing in a cathode of an electric field emission device by using a plurality of transistors connected in series to the cathode.
If a plurality of electric field emission X-ray tubes are configured using a plurality of electric field emission devices, at least two transistors are connected to each electric field emission device and each gate of the transistors is separately controlled. Therefore, a configuration of a current control circuit is complex and efficient driving is difficult.